Sounds like he's importing your files into a sketch plane in solidworks and then converting this to vector data by using autotrace options.

Edit: Would it be possible to ask him to export your file you gave him to dxf or dwg format and send it back to you?, then post that exported file here on the forum - it would be interesting to see what happens to it!

@andrew - would there be any benefit in developing/enabling QCAD to export files to either STL or STEP format? so that programs like Solidworks, Pro Engineer or Rhino could handle the import more efficently.